Firefox/60.0 remaps F9

Firefox/60.0 now maps F9 for *Reader View* thus it conflicts with CSS Reloader's default short-cut. The short-cut triggers CSS Reloader in some sites (e.g. [GitHub](https://github.com/)) and Reader View in some others (e.g. [Firefox 60 Release notes](https://www.mozilla.org/en-US/firefox/60.0/releasenotes/?utm_campaign=whatsnew&utm_medium=firefox-browser&utm_source=firefox-browser#changed)). AFAIK, it depends on whether the browser heuristics determine if the page can be made available in reader mode.

Workaround: change short-cut in add-on preferences¹.

_(¹) Any suggestion of a good unused value?_

The payload names no source files or tests. Start by locating the add-on's default shortcut and reproducing the F9 conflict in Firefox 60 on GitHub and the linked Firefox release-notes page; done means CSS Reloader and Reader View no longer compete for the same default shortcut.

Written by the indexing model from the issue text.